Zinc-toxicity enhanced the Fe-stress-response mechanism in Hawkeye (Fe-efficient) but not in PI-54619-5-1 (Fe-inefficient) soybean plant. Hawkeye plants were more effective in reducing the pH of the culture solutions and in taking up Fe than the PI plants. The drop in solution pH seems to occur cyclically in response to Fe insufficiency induced by high zinc levels. The severity and nature of stress symptoms induced by high levels of zinc depends on the plant cultivar.